Optical sheet and method of assembling liquid crystal display module using the same

ABSTRACT

The present invention relates to an optical sheet and a method of assembling a liquid crystal display module that is capable of preventing an inflow of impurities on a backlight unit, thereby minimizing screen staining caused by the impurities. An optical sheet installed between a liquid crystal display panel and a light guide member according to the present invention includes a transparent peeling sheet adhered to the front surface of the optical sheet facing the liquid crystal display panel; and a semitransparent peeling sheet stuck to the rear surface of the optical sheet facing the light guide member.

This application is a Divisional of application Ser. No. 10/322,729filed on Dec. 19, 2002, now U.S. Pat. No. 7,130,008, which claimspriority under 35 U.S.C. § 119(a) of Patent Application No. P2002-6046filed in Korea on Feb. 2, 2002, the entire contents of which are herebyincorporated by reference for which priority is claimed under 35 U.S.C.§ 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a liquid crystal display module, and moreparticularly to an optical sheet and a method of assembling a liquidcrystal display module that is capable of preventing an inflow ofimpurities on a backlight unit, thereby minimizing screen stainingcaused by the impurities.

2. Description of the Background Art

Generally, a notebook personal computer NTPC is manufactured in anotebook size to enable a user to access information during the courseof the movement. A liquid crystal module LCM is used as a display devicefor displaying information in the NTPC.

The LCM includes a liquid crystal display panel and a driving circuitpart for driving the liquid crystal display panel. The liquid crystaldisplay panel includes liquid crystal cells arranged in matrix formbetween two glass substrates and switching devices for switching asignal supplied to these liquid crystal cells. Because the LCM includesglass substrates which can be easily damaged by an external impact, acase is used to protect the outer part of the LCD in order to preventsuch damage.

Referring to FIG. 1, a conventional LCM includes a support main 14, aliquid crystal display panel 2 deposited on the support main 14, a topcase 10 covering the edge of the liquid crystal display panel 2 and thesupport main 14, and a backlight unit having a plurality of opticalsheets 32, 34, 36 and a light guide panel 24.

In the liquid crystal display panel 2, a liquid crystal is interposedbetween two glass substrates to which an upper and a lower polarizingplate 42, 40 are adhered respectively, and a thin film transistor TFTdrives each of liquid crystal cells (arranged in matrix form).

The top case 10 is bent at a right angle to cover the side surface ofthe support main 14 and the edge of the liquid crystal display panel 2.The support main 14 and the top case 10 are assembled with screws (notshown).

The support main 14 is generally made as a molding, but has recentlybeen manufactured of a metal such as aluminum Al, which has excellentheatproof against high temperature, in correspondence to a highbrightness television or a high brightness monitor. A reflecting plate26 is located at the bottom of the support main 14, and the light guidepanel 24 and the optical sheets 32, 34, 36 are deposited on top of it.The liquid crystal display panel 2 is mounted on the optical sheets 32,34, 36 in the support main 14.

The back light unit includes a lamp 2O for generating light, a lamphousing 16 shaped to adequately cover the lamp 20, a light guide panel24 for converting the incident light from the lamp 20 to the planarlight source, a reflecting plate 26 installed at the rear of the lightguide plate 24, and optical sheets on which a diffusion sheet 32, alower prism sheet 34 and an upper prism sheet 36 are sequentiallydeposited.

A cold cathode fluorescent lamp CCFL is mainly used as the lamp 20, andthe light generated at the lamp 20 is incident to the light guide panel24 through an incident surface located at the side surface of the lightguide panel 24.

The lamp housing 16 has a reflecting surface on the inside of it toreflect the light from the lamp 20 to the incident surface of the lightguide panel 24. The light guide panel 24 is manufactured in the shape ofits rear surface (being inclined) and its front surface (being flat).The reflecting plate 26 reflects the light incident to itself from therear surface of the light guide panel 24 to the light guide panel 24,thereby reducing the loss of light. That is, if the light from the lamp20 is incident to the light guide panel 24, it is reflected in a tiltangle at the rear surface (being the inclined surface) to progresstoward the front surface uniformly. At this moment, the light progressedto the lower surface and the side surface of the light guide panel 24 isreflected at the reflecting plate 26 to progress toward the frontsurface. The light passing through the light guide panel 24 is diffusedto an entire area by the diffusion sheet 32.

On the other hand, the light incident to the liquid crystal displaypanel 2 has higher light efficiency when it is incident perpendicularly.For this cause, it is desirable to deposit two forward direction prismsheets to cause the progression angle of the light coming out of thelight guide panel 24 to be perpendicular to the liquid crystal displaypanel. The light passing through the diffusion sheet 32 is incident tothe liquid crystal display panel 2 via the lower and the upper prismsheets 34, 36.

In a method of assembling such a LCM, the reflecting plate 26 is mountedon the bottom surface of the support main 14, the light guide panel 24is then mounted on the reflecting plate 26, the backlight unit includingthe diffusion sheet 32, the lower prism sheet 34 and the upper prismsheet 36 are then mounted on the light guide panel 24, and the liquidcrystal display panel 2 is then mounted on the backlight unit.

In the backlight assembling process of such an LCM, an upper and a lowerpeeling sheet 44, 46 (as shown in FIG. 2) are attached to the upperprism sheet 36 for protecting the upper prism sheet 36 itself andpreventing the inflow of impurities from the outside before the upperprism sheet 36 is mounted.

Polyethylene, (a semitransparent material) is used for the upper and thelower peeling sheet 44, 46. In the event that the upper prism sheet 36(to which the upper and the lower peeling sheet 44, 46 are adhered) ismounted on the lower prism sheet 34, firstly the lower peeling sheet 46and the upper peeling sheet 44 are peeled away from the upper prismsheet 36, and then the upper prism sheet 36 is mounted on the lowerprism sheet 34. A reason why the upper and the lower peeling sheet 44,46 are removed from the upper prism sheet 36 is because the upper andthe lower peeling sheet 44, 46 is of the semitransparent material. As aconsequence, the screen inspection of the backlight unit (describedlater) cannot be carried out.

After the upper prism sheet 36 has been mounted on the lower prism sheet34, the screen inspection of the backlight unit is carried out. Thescreen inspection of the backlight unit is performed because of possibleinflow of impurities (causing stains), or other damage such asscratches. The backlight unit is inspected in-use, with light passingthrough the light guide panel 24, the diffusion sheet 32, the lowerprism sheet 34 and the upper prism sheet 36 by driving the lamp 20.

After the completion of the screen inspection of the backlight unit, theLCM whereon the backlight unit is mounted, is packed to be transferredto a liquid crystal display panel assembling process. In the liquidcrystal display panel assembling process, the liquid crystal displaypanel 2 is mounted to correspond to the top of the light guide panel 24,the diffusion sheet 32, the lower prism sheet 34 and the upper prismsheet 36 on the support main 14.

In this manner, when assembling the conventional LCM, because the upperand the lower peeling sheet 44, 46 are removed from the upper prismsheet 36 for the screen inspection of the backlight unit mounted on thesupport main 14, the surface of the backlight unit is exposed to theoutside during the job waiting time between the assembling processes ofthe liquid crystal display panel 2. Due to the external exposure of thesurface of the backlight unit, impurities flow in from the outside ontothe surface of the backlight unit. Due to such impurities flowing intothe backlight, screen staining such as white spots and black spots occurupon driving of the conventional LCM.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoptical sheet and a method of assembling a liquid crystal display modulethat is capable of preventing an inflow of impurities on a backlightunit, thereby minimizing screen staining caused by the impurities.

In order to achieve these and other objects of the invention, an opticalsheet installed between a liquid crystal display panel and a light guidemember according to an aspect of the present invention includes atransparent peeling sheet adhered to the front surface of the opticalsheet facing the liquid crystal display panel; and a semitransparentpeeling sheet adhered to the rear surface of the optical sheet facingthe light guide member.

Herein, the material of the transparent peeling sheet is PolyethyleneTerephthalate PET.

Herein, the material of the semitransparent peeling sheet isPolyethylene.

A method of assembling a liquid crystal module according to anotheraspect of the present invention includes steps of providing an opticalsheet where a transparent peeling sheet and a semitransparent peelingsheet are adhered to the front surface and the rear surface thereofrespectively; peeling the semitransparent peeling sheet away; having therear surface of the optical sheet, from which the semitransparentpeeling sheet is peeled away, face downward and the front surface of theoptical sheet, to which the transparent peeling sheet is stuck, faceupward; and irradiating light through a light guide member to theoptical sheet, to which the transparent peeling sheet is adhered, so asto detect impurities contamination on the light guide member and theoptical sheet.

The method further includes a step of depositing at least one or moreoptical sheets between the light guide member and the optical sheet towhich the transparent peeling sheet is stuck, before peeling thesemitransparent peeling sheet away.

The method further includes steps of peeling the transparent peelingsheet away; and depositing a liquid crystal display panel to bepositioned on the front surface of the optical sheet, from which thetransparent peeling sheet is peeled away.

In the described method, the material of the transparent peeling sheetis a polyester, e.g., Polyethylene Terephthalate PET.

In the described method, the material of the semitransparent peelingsheet is a polyolefin, e.g., polyethylene, polypropylene, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the invention will be apparent from thefollowing detailed description of the embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view representing a conventional liquid crystalmodule LCM;

FIG. 2 is a perspective view representing an upper prism sheet to whichan upper and lower prism sheet are adhered;

FIG. 3 is a sectional view representing a liquid crystal moduleaccording to an embodiment of the present invention;

FIG. 4 is a perspective view representing an upper prism sheet to whicha semitransparent peeling sheet, as shown in FIG. 3, is adhered; and

FIG. 5 is a flowchart representing a method of assembling a liquidcrystal module according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

With reference to FIGS. 3 to 5, a preferred embodiment of the presentinvention is explained as follows.

Referring to FIG. 3, a liquid crystal module LCM according to anembodiment of the present invention includes a support main 64, a liquidcrystal display panel 52 deposited on the support main 64, a top case 60covering the edge of the liquid crystal display panel 52 and the supportmain 64, and a backlight unit having a plurality of optical sheets 82,84, 86 and a light guide panel 74.

In the liquid crystal display panel 52, a liquid crystal is interposedbetween two glass substrates to which an upper and a lower polarizingplate 92, 90 are adhered respectively, and a thin film transistor TFTdrives each of liquid crystal cells arranged in matrix form type.

The top case 60 is bent at a right angle to cover the side surface ofthe support main 64 and the edge of the liquid crystal display panel 52.The support main 64 and the top case 60 are assembled with screws (notshown).

The support main 64 is generally made as a molding, but recently, it hasbeen manufactured of a metal which has excellent heatproof propertiesagainst high temperature (such as aluminum Al) in correspondence to ahigh brightness television or a high brightness monitor. A reflectingplate 76 is located at the bottom of the support main 64, and the lightguide panel 74 and the optical sheets 82, 84, 86 are deposited on top ofit. The liquid crystal display panel 52 is mounted on the optical sheets82, 84, 86 in the support main 64.

The backlight unit includes a lamp 70 for generating light, a lamphousing 66 installed in a shape so as to cover the lamp 70, a lightguide panel 74 for converting the incident light from the lamp 70 to theplanar light source, a reflecting plate 76 installed at the rear of thelight guide plate 74, and optical sheets on which a diffusion sheet 82,a lower prism sheet 84 and an upper prism sheet 86 are sequentiallydeposited.

A cold cathode fluorescent lamp CCFL is mainly used as the lamp 70, andthe light generated at the lamp 70 is incident to the light guide panel74 through an incident surface located at the side surface of the lightguide panel 74.

The lamp housing 66 has a reflecting surface on the inside of it toreflect the light from the lamp 70 to the incident surface of the lightguide panel 74. The light guide panel 74 is manufactured such that theshape of its rear surface is inclined and its front surface is flat. Thereflecting plate 76 reflects the light incident to itself through therear surface of the light guide panel 74 to the light guide panel 74,thereby reducing the loss of light. That is, if the light from the lamp70 is incident to the light guide panel 74, it is reflected in a tiltangle at the rear surface, being the inclined surface to progress towardthe front surface uniformly. At this moment, the light progressed to thelower surface and the side surface of the light guide panel 74 isreflected at the reflecting plate 76 to progress toward the frontsurface. The light passing through the light guide panel 74 is diffusedto an entire area by the diffusion sheet 82.

On the other hand, the light incident to the liquid crystal play panel52 has higher light efficiency when it is incident perpendicularly. Toachieve this, it is desirable to deposit two forward direction prismsheets for the progress angle of the light coming out of the light guidepanel 74 to be perpendicular to the liquid crystal display panel. Thelight passing through the diffusion sheet 82 is incident to the liquidcrystal display panel 52 via the lower and the upper prism sheet 84, 86.

At this moment, an upper and a lower peeling sheet 94, 96 (as shown inFIG. 4) are adhered to the upper prism sheet 86 for protecting the upperprism sheet 86 itself and preventing the inflow of impurities from theoutside before the upper prism sheet 86 is mounted.

In the optical sheets according to the present invention, polyethyleneterephthalate PET, being a transparent material is used for the upperpeeling sheet 94 which is stuck to the front surface of the upper prismsheet 86. Polyethylene as a semitransparent material is used for thelower peeling sheet 96 which is (adhered) to the rear surface of theupper prism sheet 86.

In the event that the upper prism sheet 86 to which the upper and thelower peeling sheet 94, 96 are adhered is mounted on the lower prismsheet 84, only the lower peeling sheet 96 of a semitransparent materialis peeled away from the upper prism sheet 86 first, and then the upperprism sheet 86 is mounted on the lower prism sheet 84. On the otherhand, the upper peeling sheet 94 is peeled away from the upper prismsheet 86 just before assembling the liquid crystal display panel 52after the completion of the screen inspection of the backlight unit(described later).

In this assembling method of the LCM, as shown in FIG. 5, the lamphousing 66, on which the lamp 70 is mounted, is mounted on the supportmain 64 (S1).

The reflecting plate 76 and the light guide panel 74 are sequentiallymounted on the bottom surface of the support main 64 where the lamphousing 66 is mounted (S2, S3).

Then, the diffusion sheet 82 and the lower prism sheet 84 are mounted onthe light guide panel 74 (S4, S5).

Subsequently, the lower peeling sheet 96 of the upper and the lowerpeeling sheet 94, 96 adhered to the upper prism sheet 86 only isremoved, and the rear surface of the upper prism sheet 86 from which thesemitransparent peeling sheet 96 is peeled away is made to face downwardso that the front surface of the upper prism sheet 86 to which thetransparent upper peeling sheet is adhered is made to face upward, andthen the upper prism sheet 86 is mounted on the lower prism sheet 84(S6, S7).

The screen inspection of the backlight unit is carried out when theupper prism sheet 86, from which the lower peeling sheet 96 is removed,is mounted on the lower prism sheet 84 (S8). At this moment, the screeninspection of the backlight unit takes place, wherein a light isirradiated to the upper prism sheet 86 (to which the transparent upperpeeling sheet 94 is adhered) via the light guide panel 74, the diffusionsheet 82, the lower prism sheet 84, the upper prism sheet 86 and thetransparent upper peeling sheet 94 by driving the lamp 70 so as toinspect for defects such as impurities inflow stains and scratches onthe backlight unit.

When the screen inspection of the backlight unit is completed, the LCMwherein the backlight unit is mounted is packed to be transferred to theliquid crystal display panel assembly process. At this moment, the upperpeeling sheet 94, which is adhered onto the upper prism sheet 86 of thebacklight unit, is not removed. Accordingly, the inflow of theimpurities from the outside onto the backlight surface is cut off duringjob waiting time between the upper prism sheet 86 mounting process andthe liquid crystal display panel 52 mounting process by the upperpeeling sheet 96.

Then, if the backlight unit (including the upper prism sheet 86) ismounted on the support main 64, the upper peeling sheet 94 is removedfrom the upper prism sheet 86 to mount the liquid crystal display panel52 to be located over the upper prism sheet 86 (S9, S10).

Subsequently, the top case 60 is mounted on the support main 64 to coverthe edge of the support main 64 and the liquid crystal display panel 52(S11).

Accordingly, the assembly method of the LCM according to the presentinvention removes the lower peeling sheet 96 of the upper and the lowerpeeling sheet 94, 96 when mounting the upper prism sheet 86 on the lowerprism sheet 84 which is mounted on the support main 64, and then thescreen inspection of the backlight unit is carried out. The screeninspection is impossible to carry out if the upper peeling sheet is notremoved from the upper prism sheet because the upper peeling sheet ismade of semitransparent material in the screen inspection of theconventional backlight unit. However, in the present invention it ispossible to carry out the screen inspection without removing the upperpeeling sheet 94 because the upper peeling sheet 94 is made of PET, atransparent material.

On the other hand, the external impurities do not flow in to thebacklight unit between the upper prism sheet 86 mounting process and theliquid crystal display panel 52 mounting process because the upperpeeling sheet 94 adhered to the upper prism sheet 86 is removed from theupper prism sheet 86 when assembling the liquid crystal display panel52.

As described above, the optical sheet and the assembling method of theliquid crystal module using the same according to the present inventionfirst adheres the transparent peeling sheet to the upper prism sheet andthen removes the transparent peeling sheet from the upper prism sheetjust before assembling the liquid crystal display panel so that theexternal exposure time of the backlight unit is minimized to cut off theimpurities inflow onto the surface of the backlight unit, therebyminimizing the screen staining caused by impurities

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theordinary skilled person in the art that the invention is not limited tothe embodiments, but rather that various changes or modificationsthereof are possible without departing from the spirit of the invention.Accordingly, the scope of the invention shall be determined only by theappended claims and their equivalents.

1. An optical sheet comprising: a diffusion sheet; a lower prism sheeton the diffusion sheet; an upper prism sheet on the lower prism sheet; atransparent peeling sheet adhered to a front surface of the upper prismsheet; and a semitransparent peeling sheet adhered to a rear surface ofthe diffusion sheet.
 2. The optical sheet according to claim 1, whereinthe material of the transparent peeling sheet is PolyethyleneTerephthalate PET.
 3. The optical sheet according to claim 1, whereinthe material of the semitransparent peeling sheet is Polyethylene.